This invention relates to a multiple effect absorption system and, in particular, to raising the coefficient of performance (COP) of a multiple effect absorption refrigeration system.
The development of multiple effect absorption refrigeration systems places particular emphasis on triple effect systems utilizing three vapor generator and refrigerant condenser units. The generator of each unit is coupled to one or more system absorbers and the condenser of each unit, in turn, is coupled to one or more system evaporators. A triple effect system is described in U.S. Pat. No. 4,531,374 to Alefeld (FIG. 44G). The three generator and condenser units are staged so the units operate at successively higher pressures and temperatures. External heat is provided to the generator that is operating at the highest pressure and temperature to evaporate refrigerant from the absorbent solution delivered from the system absorber section. The refrigerant is condensed in the generator of the intermediate stage, thus causing additional refrigerant vapor to evolve from the intermediate stage generator. The vapor from the intermediate stage generator is condensed in the generator of the third low pressure generator. The refrigerant vapor that is produced in the third stage generator is, in turn, condensed in the third stage condenser and is flashed to the system evaporator along with that of the other two condensers to provide the refrigeration effect.
In many single and double effect absorption refrigeration systems, solution heat exchangers are provided in which energy (heat) is transferred between strong and weak absorbent solution as it moves between the system absorber and the one or more refrigerant generators. For purposes of this disclosure, absorbent solution that is rich in refrigerant will be referred to as weak solution and absorbent solution that is relatively deplete of refrigerant will be referred to as strong solution. The solution heat exchangers are employed to transfer heat from the higher temperature, relatively strong, solution streams into the lower temperature, relatively weak, solution streams so as to recover available energy present in the solution. The efficiency of these solution heat exchangers is limited by the costs involved and the system fluid handling capabilities.
In U.S. Pat. No. 5,205,136 to DeVault et al., a method for further increasing the efficiency of a triple effect absorption refrigeration cycle is disclosed. This method is referred to as double condenser coupling or simply DCC. Here, high temperature refrigerant vapor developed in the high temperature stage is condensed and used to drive the generator of the intermediate temperature stage Heat contained in the resulting liquid refrigerant is then used to drive the generator of the low temperature stage by further subcooling the liquid refrigerant. The condensate from both the intermediate temperature and low temperature generators, along with the condensate from the low temperature condenser are all expanded to the system evaporator to create the desired refrigerant effect. Although this system is an improvement over prior art triple effect systems, not all the available heat in the condensate is fully utilized within the system.
Erickson et al. in U.S. Pat. No. 5,653,116 discloses a split triple effect absorption refrigeration system containing two hermetic loops. One loop is a double effect loop while the other is a single effect loop which overlaps the high pressure section of the double effect loop. Heat exchangers are provided within the loops and between the loops for exchanging heat between weak and strong solution and between refrigerant condensate and a relatively weak solution. In one form of the system, shown at FIG. 2, the condensate developed in the second stage of the double effect loop is placed in heat transfer relationship with weak solution passing between the absorber and the low temperature generator in this loop. The condensate, after it has given up heat to the weak solution, is passed directly from the upper stage condenser directly to the low temperature stage condenser.